count 和 join 必须包含一个表中不存在于另一个表中的记录

Question

见http://sqlfiddle.com/#!2/26ee6

SELECT g.gameID, (count(h.idx)%2) as lastmove
FROM games as g
  inner join history as h on g.gameID=h.gameID 
WHERE (g.whitePlayer=2 or g.blackPlayer=2)
GROUP by g.gameID, g.whitePlayer, g.blackplayer
HAVING (g.blackPlayer=2 AND lastmove=1)
OR (g.whitePlayer=2 AND lastmove=0)

首选结果：

gameID--lastmove - really move  - is it player=2 's move ?
256 ---- null --=> white -> player2= white = yes its move => out
414 ----  1 ----=> black -> player2= white   = not
497 ----  0 --- => white -> player2= white = yes its move => out
498 ----  1 --- => black -> player2= black = yes its move => out

我正在尝试获取所有游戏

(g.blackPlayer=2 AND lastmove=1) OR (g.whitePlayer=2 AND lastmove=0)

问题在于第 256 场比赛，历史上没有记录。

(count(h.idx)%2) as lastmove  returns 0 and that is good

但 gameID 不在 Join 中，因此 gameID=256 完全错过了！

如果我反过来加入，我将无法无错误地实现 COUNT， 无论如何也错过了256场比赛：

SELECT g.gameID
FROM games as g
  inner join history as h on g.gameID=h.gameID 
WHERE (g.whitePlayer=2 or g.blackPlayer=2)
GROUP by g.gameID, g.whitePlayer, g.blackplayer
HAVING (g.blackPlayer=2 AND ((count(h.idx)%2)=1) -error
OR (g.whitePlayer=2 AND ((count(h.idx)%2)=0)  -error

http://sqlfiddle.com/#!2/26ee6

谁能帮助解决这个问题？谢谢。

Answer 1

我不是 100% 确定我理解你的问题，但如果你想包含游戏 256，你应该做一个左连接而不是内连接：

SELECT g.gameID, (count(h.idx)%2) as lastmove
FROM games AS g
  LEFT JOIN history AS h ON g.gameID=h.gameID 
WHERE (g.whitePlayer=2 OR g.blackPlayer=2)
GROUP BY g.gameID, g.whitePlayer, g.blackplayer
HAVING (g.blackPlayer=2 AND lastmove=1)
OR (g.whitePlayer=2 AND lastmove=0);

在您的第二个查询中，您缺少几个 )。

如果你用左连接来做，那就是：

SELECT g.gameID
FROM games as g
  LEFT JOIN history AS h ON g.gameID=h.gameID 
WHERE (g.whitePlayer=2 OR g.blackPlayer=2)
GROUP BY g.gameID, g.whitePlayer, g.blackplayer
HAVING (g.blackPlayer=2 AND ((count(h.idx)%2)=1))
OR (g.whitePlayer=2 AND ((count(h.idx)%2)=0))  ;

见sqlfiddle